March 26, 2020 Contributors


scope_max_outbound_connections — provide traffic shaping for outbound connections


Scope_Max_Outbound_Connections = 20


**Configuration Change. ** This feature is available as of version 3.2.

Scope_Max_Outbound_Connections provides for finer-grained manipulation of the number of outbound connections than does Server_Max_Outbound_Connections. When used in different scopes its behavior is as follows:

  • In the global scope, it behaves like Server_Max_Outbound_Connections

  • In a Global::Domain scope, it determines the maximum number of connections to the specified domain across all bindings

  • In a Binding_Group::Domain scope, it determines the maximum number of connections to the specified domain across all the bindings in that Binding Group

  • In a Binding::Domain scope, it behaves like Max_Outbound_Connections

  • In a Global::Host scope it determines the maximum number of connections to the specified host across all bindings


server_reserve_outbound_connections must be set to 0 in order for scope_max_outbound_connections to work properly in the Global::Domain scope. However, when server_reserve_outbound_connections is set to 0 and the server is under load, low volume domains may be starved of connections.

Scope_Max_Outbound_Connections is disabled by default. When it is not set then Max_Outbound_Connections or Server_Max_Outbound_Connections is used, depending on the context.

You might want to use this option in circumstances where two MX names resolve to a list of identical IP addresses. This is currently the case with and Any given sending host cannot have more than three simultaneous connections to any given host for both domains. To ensure that you are working within these parameters, use Scope_Max_Outbound_Connections in the following way:

domain "/^(wanadoo|orange)\.fr$/" {
   Scope_Max_Outbound_Connections = 3

With this configuration both domains are considered as one for the sake of total outbound connections.

To highlight how Scope_Max_Outbound_Connections differs from Max_Outbound_Connections consider the following example:

domain "/^(aol|yahoo).com$/" {
  Max_Outbound_Connections = 5

The preceding example is identical to the following configuration:

domain "" {
  Max_Outbound_Connections = 5

domain "" {
  Max_Outbound_Connections = 5

This gives a maximum of 5 outbound connections for each domain.


scope_max_outbound_connections is valid in the global, binding, binding_group, domain and host scopes.

See Also

max_outbound_connections, server_max_outbound_connections, server_reserve_outbound_connections